This application relates to an airfoil for a turbine engine, such as a turbine blade. More particularly, the application relates to cooling features provided on the airfoil.
Typically, cooling fluid is provided to a turbine blade from compressor bleed air. The turbine blade provides an airfoil having an exterior surface subject to high temperatures. Passageways interconnect the cooling passages to cooling features at the exterior surface. Such cooling features include machined or cast holes that communicate with the passageways to create a cooling film over the exterior surface.
In one example manufacturing process, a combination of ceramic and refractory metal cores is used to create the cooling passages and passageways. The refractory metal cores are used to create relatively small cooling passages, typically referred to as microcircuits. The microcircuits are typically too thin to accommodate machined cooling holes. The simple film cooling slots that are cast by the refractory metal cores can be improved to enhance film effectiveness. There is a need for improved film cooling slots formed during the casting process by the refractory metal cores to enhance film cooling effectiveness while using a minimal amount of cooling flow.
One prior art airfoil has employed a radial trench on its exterior surface to distribute cooling flow in a radial direction. However, the radial trench is formed subsequent to the casting process by applying a bonding layer and a thermal barrier coating to the exterior surface. This increases the cost and complexity of forming this cooling feature.